Method and apparatus for forming a shale cake and measuring the resistivity and density thereof

ABSTRACT

Method and apparatus for forming a shale cake of a standardized volume from random samplings of shale cuttings obtained from a well, and wherein the electrical resistivity and density of such shale cake is measured to thereby provide dependable objective data for analysis as to various conditions in the well which indicate the presence or lack of petroleum formations and pressurized layers in the well.

United States Patent Overton 1 June 27, 1972 54] METHOD AND APPARATUS FOR 2,302,996 11/1942 Lilligren ..73/1s3 FORMING A SHALE CAKE AND 1,327,806 1/1920 Bundem ....l07/17 MEASURING THE RESISTIVITY AND 1,445,789 2/ 1923 Mo onmer ..73/32 DENSITY THERE F Primary Examiner-S. Clement Swisher [72] inventor: Harold L. Overton, 5418 Whispering n p l, Wil & M tth ws Creek, Houston, Tex. 77017 22 Filed: June 22, 1970 ABSTRACT [21] Appl. No.: Method and apparatus for forming a shale cake of a standardized volume from random samplings of shale cuttings obtained from a well, and wherein the electrical resistivity and 'i "73/432 23/230 density of such shale cake is measured to thereby provide de- [58 1 i i 23/230 pendable objective data for analysis as to various conditions in l 4 R 324/13 the well which indicate the presence or lack of petroleum formations and pressurized layers in thewell.

[56] References Cited. 7 Claims, 1 Drawing Figure UNITED STATES PATENTS 2,759,148 8/ 1956 Store ..324/65 J Z 22 r A 25a J24 v 32 32%;? Z 40 -37 l J/ 36 300 *1? A 4 30c PATENTEUJUNZ'Y I872 flora/a Z. Grew fan INVENTOR nuwei MAW & MaHLeu/A ,ITTORNE YS METHOD AND APPARATUS FOR FORMING A SI'IALE CAKE AND MEASURING THE RESISTIVITY AND DENSITY THEREOF BACKGROUND OF THE INVENTION The field of this invention is methods and apparatus for treating and testing shale cuttings from a well for the purpose of locating any petroleum formations and pressurized intervals in the well. I

In the past, it has been the practice to have an operator visually inspect shale cuttings at the surface, generally at the shale shaker, and then attempt to select representative samples. The volume of the samples had to be measured, using calipers for obtaining the dimensions, so that subsequent resistivity measurements could be'adjusted to a unit volume basis mathematically. Because the selection of samples by such procedure was necessarily subjective and was limited to those cuttings of approximately the same volume, the test data obtained therefrom was subject to considerable variation and often resulted in erroneous data and conclusions, especially when the samples of shale cuttings were selected by different operators onthe same well.

SUMMARY OF THE INVENTION The present invention relates to a method .and apparatus for forming a shale cake from randomly collected shale cuttings, wherein the shale cake is formed into a standard volume, so that the problems of the prior art subjective selection and the obtaining of samples having suitable volumes have been obviated. Because the volume of each shale cake thus formed is the same as the others, the resistivity and density measurements may be used without making mathematical calculations to correct for variable volumes of-the samples as was required in the prior art.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a vertical sectional view, partly in elevation, illustrating the press means or unit utilized in carrying out part of the method of this invention and also forming part of the apparatus of this invention.

FIG. 2 is a horizontal cross-sectional view taken on line 2- 2, illustrating a removable plate forming a part of the press means ofFIG. l;

FIG. 3 is a vertical sectional view, partly in elevation, illustrating a holder ring used in holding a shale cake which has been formed in thepress means of FIG. 1 so that the ends of such cake can be trimmed flush with the ends of the holder ring; and

FIG. 4 is a schematic illustration, partly in section and partly in elevation, of the electrical arrangement for measuring the voltage drop across each shale cake.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the drawings, the letter A designates generally the press means or unit which is utilized for crushing and pressing random samples of shale cuttings into a shale cake C. The shale cake C is subsequently placed in a holder ring R so that the ends C-1 and C-2 may be trimmed off with a knife K so as to be flush with the ends of the ring R, as will be more evident hereinafter. After trimming the ends C-1 and -2 from the cake C, the cake C is then of a predetermined volume and such volume may be reproduced repeatedly with different shale cuttings.

Each successiveshale cake C thus formed is preferably weighed so as to obtain the density of the cake C. Since the I and P-l (FIG. 4), which are connected in an electrical circuit with any source of electrical power such as a battery B. The current supplied to the plates P and P-l is controlled or suitably adjusted so that it is constant for each cake C disposed between such plates, which current is indicated on an ammeter 10, while thevoltage drop across the plates P and P-l through the cake C is indicated on a volt meter 12. Since the volume of each successive cake C is the same, and the current supplied to the plates is controlled so as to be the same during each test, the voltage drop indicated at the meter 12 for eachcake C is directly proportional to the resistivity of each shale cake C and therefore, the voltage reading for each of the shale cakes C may be plotted on a graph with respect to the elevation in the well from which the shale cuttings for each cake C were obtained, so as to indicate the presence and elevation of petroleum formations and over-pressured intervals in a well, using known analysis techniques.

Considering the invention more in detail, the press means or unit A includes a cylinder 20 having a longitudinal opening 22 therethrough. The opening 22 is preferably cylindrical in shape, although its cross-sectional shape may be square or of any other desired configuration. A plunger 25 is adapted to be inserted into the open upper end of the opening 22 and it has at least a portion thereof formed with the same external shape as the internal shape of the opening 22. Therefore, in the form of the invention illustrated In FIG. I, the external surface of the plunger 25 is cylindrical and conforms substantially with the cylindrical surface of the opening 22. Preferably a seal 26, such as an O-ring formed of rubber or other suitable material is disposed in an annular groove 25a for providing a fluid-tight sealing contact between the plunger 25 and the wall of the hole 22. The upper end 25b of the plunger 25 extends above the upper end of the cylinder 20 and is preferably provided with wrench flats so that the plunger 25 may be rotated in either direction if desired. Normally, the plunger 25 is forced or moved longitudinally or vertically without rotation to accomplish the crushing and pressing of the shale cuttings into the shale cake C as will be more fully explained. Pressures in the neighborhood of 10,000 p.s.i. are applied to the plunger 25 with a hydraulic ram (not shown) or any other similar apparatus to crush and press the cuttings into the homogeneous and reconstituted cake C. v v

A removable plate 30 is disposed at one end of the cylinder 20 opposite from the end at which the plunger 25 enters the hole 22, and such plate 30 is removably positioned so that it forms a closure at such end of the opening 22. In the embodiment illustrated in the drawings (FIGS. 1 and 2),the removable plate 30 is secured to the lower end of the cylinder 20 by means of a plurality of machine bolts 31 which extend through suitableopenings 32a in a ring 32 which is releasably connected to the cylinder 20, above the plate 30. The machine bolts 31 may be threaded into the removable plate 30, or they may extend through openings 30a and extend below the plate 30 for threading into threaded openings 33a in a filter plate 33 located at the bottom of the apparatus A. As illustrated in FIG. 1, the ring 32 has internal threads 32b which are in threaded engagement with external threads 20a on the cylinder 20 so that by unthreading the threads 32b from the threads 20a, the ring 32, together with the removable plate 30 and the filter plate 33, may be removed from they cylinder 20. After the plate 30 has been thus removed from the cylinder 20, the cake C may be forced completely out of the opening 22 by forcing the plunger 25 further downwardly relative to the cylinder 20 from that position shown in FIG. 1.

Since the shale cuttings have free water therewith which may be extracted during the pressing of the shale cuttings to form the shale cake C with the press means A, means are provided with the removable plate 30 and with the filter plate 33 for removing such extracted water. Thus, a central passage 30b and outer passages 300 are provided through the plate 30. The outer passages 30c communicate with each other at their upper ends through a circular groove or recess 30d which is disposed so that it receives water which has been squeezed from the shale cuttings during the pressing thereof to form the cake C.

The upper surface of the plate 30 is preferably formed with serrations 30c. Similar serrations 25c are formed on the lower surface of the plunger 25, which serrations 25c and 30a tend to make the particles of the shale cuttings move or shift laterally as they are forced downwardly by the plunger 25, so that the final cake C is rendered homogeneous and substantially free of holes or pores.

The water or other effluent from the pressing of the shale cuttings flows downwardly through the passages 30b and 30c and is received in a central recess 33b of the filter plate 33 in which a screen 35 and a piece of filter paper 36 thereon are disposed. The filter paper 36 collects solids which pass downwardly through the passages 30b and 30c so as to prevent a clogging of a discharge port 33c formed in the filter plate 33 below the recess 33b; The screen 35 may not be required but its presence prevents a rupturing of the filter paper 36 by the pressure developed thereabove as the plunger 25 is forced downwardly. The filter paper 36 may be replaced as needed by removing the bolts 31 after the ring 33 has been disconnected from the cylinder 20.

1 Suitable seals, such as O-ring seals 40 and 41, are provided between the plate 30 and the cylinder 20 and also between the plate 30 and the filter plate 33, respectively, so that the water or other effluent which is squeezed from the shale cuttings during the pressing thereof to form the cake C will not escape except through the discharge port 330.

The holder ring R has a longitudinal opening 42 therethrough which has a diameter equal to, or slightly larger than, the diameter of the opening 22 so that the shale cake C may be positioned in the opening 42 after it has been forced out of the longitudinal opening 22 by the plunger 25, as will be explained. For ease of insertion and removal, the diameter of the opening 42 is preferably slightly larger than the diameter of the opening 22, as will be understood, but such diameters should be approximately the same to facilitate the cutting of the ends C-1 and C-2 from the cake C, using a knife K or any other suitable cutting means so as to cut the ends of the cake C flush with the ends 43 and 44 of the ring R. After the ends C-1 and C-2 havebeen cut from the cake C, the cake C then has a predetermined or standardized volume which may be duplicated for each of the subsequent shale cakes C which are reconstituted in the press means A. The standard volume cake C is then disposed between the plates P and P-l as illustrated schematically in FIG. 4 for obtaining the voltage drop thereacross with a constant current supplied to the plates from any suitable source of power B.

in carrying out the method of this invention, samples of shale cuttings are initially collected from a conventional shale shaker or at any other location where the shale cuttings are returned from a well bore which is being drilled. The shale cuttings are selected at random from the mass thereof so that representative objective samples of the shale cuttings are thus obtained. The samples of the shale cuttings which have thus been randomly collected for a particular elevation in the well are dropped into the longitudinal opening 22 with the plunger removed from such opening 22. The removable plate is secured to the lower end of the cylinder 22 so as to form a closure at the bottom thereof as indicated in FIG. 1. After a predetermined quantity of the shale cuttings has been placed in the opening 22, the plunger 25 is then forced downwardly on the cuttings to crush and press the cuttings to a reduced thickness and reconstituting them as the shale cake C. During such pressing and crushing action, the free water is forced or is extracted from the shale cuttings and is caused to flow through the ports or passages 30b and 30c to the filter plate 33 below where the effluent is discharged through the drain port 330.

With the method of this invention, substantially all of the free water is thus extracted from the shale, leaving essentially only the crystalline and bound water with the shale. The effluent may be collected at the discharge from the port 330 for conducting electrical tests or other tests thereon for such data as may be desired. The serrations 25c and 30: cause the shale particles to shift or move laterally relative to each other as the plunger 25 is forced vertically or longitudinally downwardly relative to the plate 30 which forces the particles into a homogeneous cake substantially without any pores or openings therethrough.

After the shale cake C has thus been formed with the shale cuttings from a particular elevation in the well, the ring 32 is unthreaded from the cylinder 20, thereby disconnecting the plate 30 from the cylinder 20 and opening the lower end of the opening 22. At that point, the ring R is placed below the cylinder 20 with the opening 42 axially aligned with the opening 22, so that upon a subsequent downward movement of the plunger 25, the cake C is forced outwardly from the opening 22 and into the opening 42.

Since the cake C has been formed under high pressures in the press means A, it is a solid wafer which will not easily fall apart or shatter into pieces. Therefore, it may be either pushed directly into the hole 42 or it may be handled and moved to the holder ring R where it is inserted into the opening 42. in either event, the ends C-l and C-2 project from the ends 43 and 44 of the holder ring R for subsequent trimming. As shown in FIG. 3, the end 0-! is dotted since it has already been removed with the knife K, and the end C-2 is in the process of being removed with the knife K so that the remaining ends of the cake C are flush with the surfaces 43 and 44 of the ring R, and thus, the predetermined volume of the cake C has been obtained.

At that point, the cake C is removed from the opening 42 and is weighed on a scale of any conventional construction (not shown). Since the volume of successive cakes thus obtained is the same, the weight of each successive cake C is directly proportional to the density of each cake C. Therefore, it is unnecessary to calculate the density for each cake C, but instead, the weights themselves may be utilized for plotting a graph or for other purposes in geologically predicting the presence and elevation of petroleum formations in a well from which the cuttings came.

Additionally, each shale cake C which is thus formed is disposed between electrical conductor plates P and P-l which may be made of silver or other similar material, and such plates are connected in the electrical circuit schematically shown in FIG. 4 so that a constant current indicated at the ammeter 10 is provided. The voltage drop across each successive cake C is indicated at the voltmeter 12. Since the resistivity of the shale cake C is mathematically equal to its electrical resistance multiplied by its cross-sectional area and divided by its length, the resistivity becomes directly proportional to the voltage drop indicated on the meter 12 since the volume of the cake C and the current are both constant for each cake C.

In carrying out the method of this invention, successive shale cakes C are formed in the press means A from samples of shale cuttings which are obtained at different elevations during the drilling of a well. Therefore, the successive shale cakes C which are produced are representative of the shale at the elevation from which they were obtained. The data, such as the density and the resistivity of the shale cakes C made from the shale cuttings acquired at the different elevations, thus provides an indication of the condition of the well and particularly the presence or lack of petroleum formations at the various elevations in the well. Known procedures are utilized in correlating and/or graphically representing the information thus obtained so as to predict the presence and elevation of petroleum formations in the well.

The foregoing disclosure and description of the invention are illustrative and explanatory thereof, and various changes in the size, shape, and materials as well as in the details of the illustrated construction may be made without departing from the spirit of the invention.

1 claim:

1. A method of obtaining statistically dependable and representative samples of shale cuttings for obtaining objective data for analysis, comprising:

collecting samples of shale cuttings at random from a mass of same;

pressing a quantity of the samples into a press to form a reconstituted shale cake;

removing the shale cake from the press;

thereafter trimming the ends of the shale cake to produce a predetermined volume;

thereafter collecting other samples of shale cuttings at random from a mass of same; and

performing said pressing, removing and trimming of the subsequently collected samples into successive shale cakes, each of which has the same predetermined volume.

2. The method set forth in claim 1, including the step of:

measuring the voltage drop across each of the shale cakes with a constant current supplied thereto for thereby obtaining voltage readings which are directly proportional to the resistivity of each shale cake.

3. The method set forth in claim 1, including the step of:

weighing each shale cake for thereby obtaining the relative densities of each shale cake. 7

4. The method set forth in claim 1 including the step of:

extracting free water from the shale cuttings as they are pressed into each shale cake to thereby obtain a shale cake which is essentially free of all water except crystalline and bound water in the shale.

5. An apparatus for obtaining statistically dependable and representative samples of shale cuttings for obtaining objective data for analysis, comprising:

press means for pressing a quantity of samples of shale cuttings into a reconstituted shale cake; means with said press means for removing the shale cake from said press means; and means for extracting free water from the shale cuttings as they are pressed into a shale cake by said press means to thereby obtain a shale cake which is essentially free of all water except crystalline and bound water in the shale. 6. The structure set forth in claim 5, wherein said press means includes:

a cylinder having a longitudinal opening therethrough, a removable plate releasably positioned at one end of said cylinder; and a plunger slidably disposed in said longitudinal opening from the other end thereof and having at least a portion thereof formed with a diameter substantially equal to the diameter of said opening for pressing shale cuttings against said plate. 7. The structure set forth in claim 6, wherein: the opposing faces of said plate and said plunger have serrations thereon to facilitate movement of the shale particles as they are pressed together to thereby assure the formation of a homogeneous substantially non-porous shale cake.

l I! i l t 

1. A method of obtaining statistically dependable and representative samples of shale cuttings for obtaining objective data for analysis, comprising: collecting samples of shale cuttings at random from a mass of same; pressing a quantity of the samples into a press to form a reconstituted shale cake; removing the shale cake from the press; thereafter trimming the ends of the shale cake to produce a predetermined volume; thereafter collecting other samples of shale cuttings at random from a mass of same; and performing said pressing, removing and trimming of the subsequently collected samples into successive shale cakes, each of which has the same predetermined volume.
 2. The method set forth in claim 1, including the step of: measuring the voltage drop across each of the shale cakes with a constant current supplied thereto for thereby obtaining voltage readings which are directly proportional to the resistivity of each shale cake.
 3. The method set forth in claim 1, including the step of: weighing each shale cake for thereby obtaining the relative densities of each shale cake.
 4. The method set forth in claim 1 including the step of: extracting free water from the shale cuttings as they are pressed into each shale cake to thereby obtain a shale cake which is essentially free of all water except crystalline and bound water in the shale.
 5. An apparatus for obtaining statistically dependable and representative samples of shale cuttings for obtaining objective data for analysis, comprising: press means for pressing a quantity of samples of shale cuttings into a reconstituted shale cake; means with said press means for removing the shale cake from said press means; and means for extracting free water from the shale cuttings as they are pressed into a shale cake by said press means to thereby obtain a shale cake which is essentially free of all water except crystalline and bound water in the shale.
 6. The structure set forth in claim 5, wherein said press means includes: a cylinder having a longitudinal opening therethrough, a removable plate releasably positioned at one end of said cylinder; and a plunger slidably disposed in said longitudinal opening from the other end thereof and having at least a portion thereof formed with a diameter substantIally equal to the diameter of said opening for pressing shale cuttings against said plate.
 7. The structure set forth in claim 6, wherein: the opposing faces of said plate and said plunger have serrations thereon to facilitate movement of the shale particles as they are pressed together to thereby assure the formation of a homogeneous substantially non-porous shale cake. 